Sources say Facebook's Project Titan may be preparing for a clash with Google's own email giant, Gmail. (Source: Warner Brothers)

The company sent out special invites on Friday to a Monday event. (Source: Facebook via TechCrunch)

Facebook rumored to have been secretly been developing the service since the start of the year

The web email market is pretty packed these days. Exact estimates of market share are problematic, as they're typically gathered by client image loads, hence minimizing the market share of clients like Google's Gmail. Currently, though, most experts agree that Google's Gmail, Yahoo! Mail, Hotmail, and Apple Mail are the big four of the e-mail world (AOL Mail still has a pretty loyal following as well).

Facebook announced on Friday that it was holding a special event on Monday, November 15, 2010 at St. Regis Yerba Buena Terrace in San Francisco. The invite has a number of hints that the event might be something email-related, with comment bubbles and a mail-stationary like background.

Reportedly the social networking giant will be announcing a full-fledged, stand-alone email client, similar to Gmail, complete with @facebook.com addresses. The full-fledged client The client has been in development since at least February of this year, under the code-name Project Titan.

If that proves true the code-name would seem appropriate as the ensuing competition would indeed be a clash of the titans as the internet's two hottest properties -- Facebook and Google -- wage war.

So will Facebook release the Kraken (e.g. the "Gmail Killer" that employees have been bragging about)? We'll have to wait until next Monday to hear for sure.